The present invention relates to a magnetic core and an induction device.
A ferrite material whose magnetic permeability is high and a dust material whose magnetic permeability is low are used as materials for a core of an induction device. In using a core made of a ferrite material, when a gap is provided for the core so as to optimize the magnetic resistance required for assuring the DC superposition characteristic, the loss is increased by magnetic flux due to the gap. On the other hand, when a core made of a dust material is used and the number of winding turns of a coil around the core is increased, the conduction loss is increased due to the large number of winding turns of the coil.
Japanese Unexamined Patent Application Publication 2002-57039 discloses a magnetic core that is made of a plurality of different materials, i.e., ferrite and dust, dispenses with the gap for the core and decreases the number of winding turns of the coil around the core.
When a core is made of a plurality of different materials, i.e., ferrite and dust, the DC superposition characteristic is determined by the saturation magnetic flux densities of the ferrite core and the dust core. Since the saturation magnetic flux density of the ferrite core is smaller than that of the dust core, the area of the cross-section of the ferrite core needs to be increased. The upper drawing of FIG. 14 shows a magnetic core composed of a dust core 200 and a ferrite core 201 having substantially the same cross sectional areas t10 and t11, respectively. In such magnetic core, increasing the cross sectional areas t10, t11 of the respective cores 200, 201 will increase the size of the magnetic core as a matter of course. For reducing the size of the magnetic core, the dust core 200 may be made with a decreased cross sectional area relative to the ferrite core 201, as shown by the dust core 202 and the ferrite core 203 in the lower drawing of FIG. 14. In such magnetic core, however, the area of contact between the ferrite core 203 and the dust core 202 is decreased due to the decreased cross sectional area of the dust core 202, with the result that the DC superposition of the coil cannot be optimized.
The present invention is directed to providing a magnetic core and an induction device which can be made small while maintaining the desired DC superposition characteristic.